Dung Beetle Navigation

Dung beetles use the Milky Way to roll their dung balls in a straight line.

Transcript

Dung beetles, looking up. I’m Bob Hirshon and this is Science Update.

The humble dung beetle, best known for rolling around balls of poop, now has a more lofty distinction. It’s the first creature known to use the Milky Way as a compass. Biologist Marie Dacke, of Lund University in Sweden, says her team wanted to know how the beetles roll their dung balls in a straight line at night. So they brought the bugs to a planetarium.

Dacke:And here, we could now dictate and say, okay, we want the eighteen brightest stars, or we want the four thousand dimmest stars, or we want only the Milky Way. And if we showed them the whole starry sky or the Milky Way, the beetles did equally well. And this is what told us the beetles are using the Milky Way for their orientation.

Although they’re the first animal proven to do so, Dacke says there are probably many others out there that we just haven’t studied closely enough. I’m Bob Hirshon for AAAS, the Science Society.

Making Sense of the Research

From a human perspective, dung beetles have a pretty disgusting lifestyle. Their diet consists almost exclusively of animal feces. To make sure they have a steady supply, they collect it and roll it into balls, which they can bury for later or keep with them for snacking. When they're feeling romantic, they'll also mate underground with a dung ball, so the female can lay her eggs in it.

A less icky but impressive characteristic of dung beetles is their ability to roll dung balls in a straight line. Many live in deserts, grasslands, or other environments with relatively few landmarks to navigate by. It was already known that the beetles could use the night sky to navigate, since they need clear skies to roll their balls in a straight line by night.

The question Dacke's team asked is: which component of the night sky are the dung beetles using? The obvious answer would be either the moon or the configuration of the stars, and that's what's been assumed. But to find out for sure, they took the dung beetles into a model environment where they could control the night sky: a planetarium.

The results were surprising. Although the beetles, as expected, were able to navigate by the entire starry sky, they were also equally successful using just the Milky Way. The Milky Way is the galaxy that the sun, Earth, and our solar system are located in. We can see part of it because the entire Milky Way is shaped like a disk, and our solar system is located relatively close to one edge of it. So when we look toward the center, we can see a flat cross-section of the rest of the disk.

In the night sky, the Milky Way appears as a blurry, narrow, pale band. It's blurry and relatively dim because we're looking at a thick layer of stars, many of which are too far to see individually. In fact, we can only see any light at all from just part of the Milky Way—the actual center is too far away, let alone the opposite edge. For this reason, the Milky Way is also visible only on clear nights, in places far from artificial light. So it's not visible from major cities or nearby areas.

Back to the dung beetles: When the researchers adjusted the planetarium so that it showed only the pale band of the Milky Way, and not any stars that were close enough to be seen as individual points of light, the beetles still rolled the ball in a straight line. That proves that they can use, to some extent, the alignment of the Milky Way to keep their dung ball on course. It's the first creature ever shown to use the Milky Way itself, but the researchers suspect there are many others out there. We just haven't identified them yet, or we've discovered that they use the night sky to navigate and left it at that.

Now try and answer these questions:

How do we know dung beetles use the night sky to navigate?

Why did the researchers go to a planetarium to study this more closely?

How did they prove that the beetles use the Milky Way, itself, to get their bearings?

Why is it reasonable to assume that other animals can do this?

You may want to check out the GoSkyWatch Planetarium App, which allows you to identify and locate stars, planets, constellations, and more by touching the screen or by pointing it to the sky.